Preparation of titanium oxide



Patented July 28, 1942 PREPARATION OF TITANIUM OXIDE Fredric C. Verduin,Audubon, N. J., assignor to The Sherwin-Williams Company, Cleveland,Ohio, a corporation of Ohio No Drawing.

Application April 6, 1940,

Serial No. 328,375

7 Claims.

The present invention relates to titanium dioxide pigments and hasspecial reference to pigments prepared from aqueous solutions of simpleor complex titanium fluoride compounds. Such solutions are obtained bythe action of fluorine, hydrofluoric acid, or a reactive fluoride, suchas ammonium fluoride, on ilmenite, rutile, or other titaniferousmaterial.

This application is a continuation in part of application Serial No.236,067, filed October 20, 1938, on which Patent No. 2,232,817 wasissued February 25, 1941'.

The fluoride solutions of titanium differ from the correspondingsulphate and chloride solutions in possessing a relatively greaterstability as exhibited by their greatly reduced tendency to hydrolyzeunder thermal treatment or dilution. Two examples which show thisstability are given so that those familiar with titanium chemistry willrecognize this unusual property. If 1 cc. of an ilmenite sulphatesolution containing 8% TiOz, 16% H2304, 14% FeSO4 be diluted to 1000 cc.with distilled water, rapid hydrolysis occurs and on standing a whiteflocculate'd pre-.

cipitate forms from the milkyliquid. If 1 cc. of a complextitanium-ammonium-fluoride solution of the composition 8% TiOz, 11% NHa,and 20% F be diluted to 1000 cc. with distilled water no precipitatewill be observed;

As a second example, if these two solutions are refluxed, the sulphatesolution will begin to develop a hydrolysis of titania within an hour,proceeding substantially to completion in four hours, whereas thefluoride solution will show no hydrolysis even after a considerablylonger period of time.

In order to obtain hydrates from one of the types of fluoride solutionsmentioned above, it is necessary to maintain a pH higher than 7.0 by

the use of an alkali. In general the hydrolyzing agent used is aqueousammonia, the use-of the alkali metal hydroxides being complicated by theadsorption of alkali metal ions on the hydrate or by the formation ofinsoluble complexes.

By obtaining complex fluoride solutions containing substantially onlyfluorine, titanium, and ammonium complexes, and with all the impuritiesreduced -to a minimum by known methods,

and by using pure ammonium hydroxide to effect precipitation, titaniahas been produced consistently by me in a coagulated filterable form.Such precipitates have been washed and calcined to a pigment which canbe compared favorably with current titanium pigments ofierecl forsale.

pigments is greater than the average product, due to quantities ofrutile which are formed in the pigment during calcination.

This invention relates to the discovery that by the use of certainagents" hereinafter termed flocculents" and which may be added either tothe titanium solution or to the ammonia, the titania hydrate precipitateis non-peptized and is caused to coagulate or flocculate even moreintensely with the result that it is easily filterable and theefficiency of washing greatly improved:

thus a purer. product is obtained by the use of my novel fiocculent,which product will withstand calcination at a higher temperature thanhas been possible heretofore without deterioration of color. This highertemperature favors the formation of rutile and the accompanying superiorpigment properties. Those familiar with'the art will recognize that manyimpurities, even in small amounts, greatly reduce the maximumtemperature permissible during calcination.

These flocculents have been found to include all dibasic and polybasicacids and their salts, provided such acids or salts will yield either adibasic orpolybasic acid radical or a divalent or polyvalent ion in theammonia or titanium solution. Special preference is given to the freeacids such as sulphuric acid, phosphoric acid, oxalic, citric, arsenic,and tartaric, and to the ammonium salts thereof and to ammoniumcarbonate, but naturally I am not limited to these alone. I realize thatusing alkali metal salts may cause the precipitation of simple orcomplex alkali metal fluorides which are not easily soluble and culatoris either to the tiania solution, or to the ammonia, I do not wish to belimited to this par ticular method. For example, I may add theflocculator to the mixture after the precipitation of the titania, orthe flocculator may be added to the ore, or at any place thereafter upto the The tinting strength and hiding power of these time of filteringthe hydrated titania.

While the preferred method of adding the fioc- Only a relatively smallamount of the floccu later is required and, generally, the amount isabout 1% or less, based on the weight of T102 present in the titaniasolution, as will be noted from the following illustrative examples ofthe use of certain fiocculators which are more or less typical of thegroup above specified.

Example I To 10 kilograms of a complex titanium-ammonium-fiuoridesolution, prepared :by digesting ilmenite with an excess of ammoniumfluoride according to the method disclosed by Svendsen, U. S. 2,042,435,and suitably purified, and containing 800 grams of TiOz add 4 grams ofsodium sulphate. This mixture is run into 50 kilograms of 10% ammoniumhydroxide solution over a period of\40 minutes. The highly fiocculatedhydrated titania is then washed free from adhering impurities andcalcined for two hours at 1000 C. The product is very white pigmentaryrutile.

Example Ii 'Io 1000 pounds of titanium-ammonium fiuoride solutioncontaining 80 pounds of titanium dioxide is added 0.298 pound ofammonium phosphate. This solution is then slowly added to 5000 Example III To 10,000 pounds of 5% ammonia add 0.4 pound oxalic acid crystals.During one hour add 1000 pounds of titanium-ammonium-fiuoride solution,containing 65 pounds of titanium dioxide. with constant stirring.

hydrate very rapidly settles, due to the intense coagulating action ofthe phosphate ion. and may be filtered and washed tree from fluorine andother undesirable soluble impurities. The bydrate is then dried andcalcined at a high temperature (800 to 1000 C.) until the optimumpigment properties of rutile are obtained. These properties and theirdependency on temperature of 'calcination are influenced greatly by thepresence of phosphate ion.

\. Example V -To 8 kilograms of a complex titanium-ammonium-fluoridesolution, prepared by digesting ilmenite with an excess of ammoniumfluoride according to the method disclosed by Svendsen, U. S. 2,042,435,and suitably purified, and containing 800 grams of TiO: add 2.6 grams of85% phosphoric acid. This mixture is run into 32 kilograms of 20%ammonium hydroxide solution ,over a period of 40 minutes. The highlynocculated hydrated titania is then washed free from adhering impuritiesand calcined for two hours at 1000 C. The product is very whitepigmentary rutile.

While the above examples illustrate various ways of practicing myinvention, it will be understood that the scope of the invention is notlim- The precipitated hydrate is then filtered,

washed, and calcined at from 800 C. to 1000 C. until the pigmentaryrutile is formed.

, Example IV One kilogram of ilmenite containing 53% of TiOz is heatedwith 6 kilograms of a 50% solution of ammonium fluoride until the masshas become heavy and pasty. The mass is diluted .to 6% TiOzconcentration and settled, and the titanium-ammonium-fiuoride solutionremoved by decantation and the excess acidity neutralized with ammonia.To the solution at 50 C. is added ammonium sulphide to the extent of0.12 kilo of ammonium sulphide per kilo of titanium dioxide in solution.The black liquor is filtered and-then a further clarification is erfected using 25 grams of trisodium phosphate dissolved in water per kiloof titanium dioxide in solution. The sodium ions immediately formtitanium fluorine complexes which are sparingly soluble and crystallizeout as an easily filterable material. During the formation andcrystallization of these. complexes residual amounts of impurities arealso precipitated ,or occluded and removed from the solution. Instead oftrisodium ted to the use of the particular fiocculents or the ethodsdescribed therein but includes all fiocculents and methods as defined inthe appended claims.

Having thus described my invention I claim:

1. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which comprises hydrolytically precipitatingnonpeptized, easily filterable, hydrous titanium oxide from an aqueoussolution of a titanium tetrafiuoride compound to which has been added asmall amount of a compound selected from the group consisting of theacids and alkali metal salts of the citrate, 'arsenate, and carbonateradicals, separating the said hydrous titanium oxide and calcining it torutile crystalline structure.

2. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which comprises contacting an aqueous solution ofa titanium tetrafluoride compound containing a small amount of acompound selected from the group consisting of the acids and alkalimetal salts of the citrate, arsenate, and carbonate radicals with anaqueous solution or ammonia to hydrolytically precipitate non-peptized,easily filterable, hydrous titanium oxide, separating the said hydroustitanium oxide and calcining it to rutile crystalline structure.

3. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which comprises hydrolytically precipitatingnon-peptized, easily filterable, hydrous titanium oxide from an aqueoussolution oila titanium tetrafiuoride compound containing about 1% orless of a compound selected from the group consisting of the acids andalkali metal salts of the citrate, arsenate and carbonate radicals,based on weight of T102 contained in the said solution, separating thesaid hydrous titanium oxide and calcin ing it to rutile crystallinestructure.

4. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which comprises contacting an aqueous solution ofa titanium tetrafluoride compound to which has been added about 1% basedon the weight of T10: of a compound selected from the group conslstingof the acids and alkali metal salts of the citrate, arsenate, andcarbonate radicals with an aqueous solution of ammonia to hydrolyticallyprecipitate non-peptized, easily v filterable, hy-

drous titanium oxide, separating the said hydrous titanium oxide andcalcining it to rutile crystalline structure.

5. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which comprises hydrolytically precipitatingnon-peptized, easily filterable, hydrous titanium oxide from an aqueoussolution of a complex titaniumammonium-fiuoride compound containing asmall amount of a compound selected from the group consisting of theacids and alkali'metal salts of the citrate, arsenate, and carbonateradicals, separating the said hydrous titanium oxide and calcining it'to rutile crystalline structure.

6. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which 20 comprises contacting an aqueous solutionof a complex titanium-ammonium-fiuoride compound to which has been addeda small amount of a compound selected from the group consisting of theacids and alkali metal salts of the citrate, arsenate, and carbonateradicals with an aqueous solution of ammonia to hydrolytically precipi-I tate' non-peptized, easily, filterable, hydrous titanium oxide,separating the said hydrous titanium oxide and calcining it to rutilecrystalline structure. i

'7. Process for the preparation of pure titanium dioxide having rutilecrystalline structure which comprises hydrolytically precipitatingnon-peptized, easily filterable, hydrous titanium oxide from an aqueoussolution of a complex titaniumammonium-fiuoiride containing about 1% orless of a compound selected from the group consist ing of the acidsandalkali metal salts of the citrate, arsenate, and carbonate radicals,based on weight of TiOz contained in the said solution separating thesaid hydrous titanium oxide and calcining it to rutile crystallinestructure FREDRIC C. VERDUIN.

